How do I get missing prototype warnings from g++?

Question

I currently have a project that uses g++ to compile it's code. I'm in the process of cleaning up the code, and I'd like to ensure that all functions have prototypes, to ensure things like const char * are correctly handled. Unfortunately, g++ complains when I try to specify -Wmissing-prototypes:

g++ -Wmissing-prototypes -Wall -Werror -c foo.cpp
cc1plus: warning: command line option "-Wmissing-prototypes" is valid for Ada/C/ObjC but not for C++

Can someone tell me:
1) Why does gcc this isn't valid? Is this a bug in gcc?
2) Is there a way to turn on this warning?

EDIT: Here's a cut and paste example:

cat > foo.cpp <<EOF
void myfunc(int arg1, int arg2)
{
    /* do stuff with arg1, arg2 */
}
EOF
g++ -Wmissing-prototypes -c foo.cpp  # complains about not valid
g++ -c foo.cpp                       # no warnings
# Compile in C mode, warning appears as expected:
g++ -x c -Wmissing-prototypes -c foo.cpp

Answer 1

-Wmissing-prototypes is not applicable for C++, because C++ always requires prototypes.

Take the following declaration for example:

void foo();

• In C, foo can be called with any number and type of arguments.
• In C++, foo does not take any arguments (compilation error if any arguments passed in).

Answer 2

Did you try -Wmissing-declarations? That seems to work for g++ and detect the error case you describe. I'm not sure which version they added it in, but it works for me in 4.3.3.